Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor device includes a substrate, a first dielectric fin, a semiconductor fin, a metal gate structure, an epitaxy structure, and a contact etch stop layer. The first dielectric fin is disposed over the substrate. The semiconductor fin is disposed over the substrate, in which along a lengthwise direction of the first dielectric fin and the semiconductor fin, the first dielectric fin is in contact with a first sidewall of the semiconductor fin. The metal gate structure crosses the first dielectric fin and the semiconductor fin. The epitaxy structure is over and in contact with the semiconductor fin. The contact etch stop layer is over and in contact with first dielectric fin.

PRIORITY CLAIM AND CROSS-REFERENCE

The present application is a Divisional application of U.S. applicationSer. No. 16/713,199, filed on Dec. 13, 2019, now U.S. Pat. No.11,004,960, issued on May 11, 2021, which is a Continuation applicationof U.S. application Ser. No. 15/635,337, filed on Jun. 28, 2017, nowU.S. Pat. No. 10,510,873, issued on Dec. 17, 2019, which is hereinincorporated by reference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. In the course of IC evolution, functional density (i.e., thenumber of interconnected devices per chip area) has increased whilegeometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess increases production efficiency and lowers associated costs.

Such scaling down has also increased the complexity of processing andmanufacturing ICs and, for these advances to be realized, similardevelopments in IC processing and manufacturing are desired. Forexample, a three dimensional transistor, such as a fin-like field-effecttransistor (FinFET), has been introduced to replace a planar transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a circuit diagram of a six transistor (6T) SRAM cell.

FIGS. 2A to 14A are perspective views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the present disclosure.

FIGS. 2B to 14B are top views of FIGS. 2A to 14A, respectively.

FIGS. 2C to 14C are perspective views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the present disclosure.

FIGS. 2D to 14D are top views of FIGS. 2C to 14C, respectively.

FIG. 8E is a cross-sectional view cut from line E-E of FIG. 8C.

FIG. 8F is a cross-sectional view cut from line F-F of FIG. 8C.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The fins may be patterned by any suitable method. For example, the finsmay be patterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins.

The present disclosure will be described with respect to embodiments, astatic random-access memory (SRAM) formed of fin field effecttransistors (FinFETs). The embodiments of the disclosure may also beapplied, however, to a variety of integrated circuits. Variousembodiments will be explained in detail with reference to theaccompanying drawings.

Static random-access memory (SRAM) is a type of volatile semiconductormemory that uses bistable latching circuitry to store each bit. Each bitin an SRAM is stored on four transistors (PU-1, PU-2, PD-1, and PD-2)that form two cross-coupled inverters. This SRAM cell has two stablestates which are used to denote 0 and 1. Two additional accesstransistors (PG-1 and PG-2) serve to control the access to a storagecell during read and write operations.

FIG. 1 is a circuit diagram of a six transistor (6T) SRAM cell. The SRAMcell 500 includes a first inverter 502 formed by a pull-up transistorPU-1 and a pull-down transistor PD-1. The SRAM cell 500 further includesa second inverter 504 formed by a pull-up transistor PU-2 and apull-down transistor PD-2. Furthermore, both the first inverter 502 andsecond inverter 504 are coupled between a voltage bus Vdd and a groundpotential Vss. In some embodiments, the pull-up transistor PU-1 and PU-2can be p-type metal oxide semiconductor (PMOS) transistors while thepull-down transistors PD-1 and PD-2 can be n-type metal oxidesemiconductor (NMOS) transistors, and the claimed scope of the presentdisclosure is not limited in this respect.

In FIG. 1, the first inverter 502 and the second inverter 504 arecross-coupled. That is, the first inverter 502 has an input connected tothe output of the second inverter 504. Likewise, the second inverter 504has an input connected to the output of the first inverter 502. Theoutput of the first inverter 502 is referred to as a storage node 503.Likewise, the output of the second inverter 504 is referred to as astorage node 505. In a normal operating mode, the storage node 503 is inthe opposite logic state as the storage node 505. By employing the twocross-coupled inverters, the SRAM cell 500 can hold the data using alatched structure so that the stored data will not be lost withoutapplying a refresh cycle as long as power is supplied through Vdd.

In an SRAM device using the GT SRAM cells, the cells are arranged inrows and columns. The columns of the SRAM array are formed by a bit linepairs, namely a first bit line BL and a second bit line BLB. The cellsof the SRAM device are disposed between the respective bit line pairs.As shown in FIG. 1, the SRAM cell 500 is placed between the bit line BLand the bit line BLB.

In FIG. 1, the SRAM cell 500 further includes a first pass-gatetransistor PG-1 connected between the bit line BL and the output 503 ofthe first inverter 502. The SRAM cell 500 further includes a secondpass-gate transistor PG-2 connected between the bit line BLB and theoutput 505 of the second inverter 504. The gates of the first pass-gatetransistor PG-1 and the second pass-gate transistor PG-2 are connectedto a word line WL, which connects SRAM cells in a row of the SRAM array.

In operation, if the pass-gate transistors PG-1 and PG-2 are inactive,the SRAM cell 500 will maintain the complementary values at storagenodes 503 and 505 indefinitely as long as power is provided through Vdd.This is so because each inverter of the pair of cross coupled invertersdrives the input of the other, thereby maintaining the voltages at thestorage nodes. This situation will remain stable until the power isremoved from the SRAM, or, a write cycle is performed changing thestored data at the storage nodes.

In the circuit diagram of FIG. 1, the pull-up transistors PU-1, PU-2 arep-type transistors. The pull-down transistors PD-1, PD-2, and thepass-gate transistors PG-1, PG-2 are n-type transistors. According tovarious embodiments, the pull-up transistors PU-1, PU-2, the pull-downtransistors PD-1, PD-2, and the pass-gate transistors PG-1, PG-2 can beimplemented by FinFETs.

The structure of the SRAM cell 500 in FIG. 1 is described in the contextof the 6T-SRAM. One of ordinary skill in the art, however, shouldunderstand that features of the various embodiments described herein maybe used for forming other types of devices, such as an 8T-SRAM memorydevice, or memory devices other than SRAMs. Furthermore, embodiments ofthe present disclosure may be used as stand-alone memory devices, memorydevices integrated with other integrated circuitry, or the like.Accordingly, the embodiments discussed herein are illustrative of waysto make and use the disclosure, and do not limit the scope of thedisclosure.

FIGS. 2A to 14A are perspective views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the present disclosure. FIGS. 2B to 14B are top views ofFIGS. 2A to 14A, respectively. FIGS. 2C to 14C are perspective views ofa method for manufacturing a semiconductor device at various stages inaccordance with some embodiments of the present disclosure. FIGS. 2D to14D are top views of FIGS. 2C to 14C, respectively.

Reference is made to FIGS. 2A to 2D. The semiconductor device includes alogic circuit region and an SRAM circuit region. In the followingdescription, the logic circuit region is referred to as LOGIC region 10,and the SRAM circuit region is referred to as SRAM region 20. FIGS. 2Aand 2B illustrate the LOGIC region 10 of the semiconductor device to beformed, and FIGS. 2C and 2D illustrate the SRAM region 20 of thesemiconductor device to be formed.

A substrate 100 is provided. It is noted that, in some embodiments, theLOGIC region 10 and the SRAM region 20 are formed on the samesemiconductor device. That is, the substrates 100 respectively describedin FIGS. 2A and 2C are different regions of the same substrate. However,in some other embodiments, the LOGIC region 10 and the SRAM region 20 ofthe semiconductor device may also be formed on different substrates.

The substrate 100 may be a bulk silicon substrate. Alternatively, thesubstrate 100 may include an elementary semiconductor, such as silicon(Si) or germanium (Ge) in a crystalline structure; a compoundsemiconductor, such as silicon germanium (SiGe), silicon carbide (SiC),gallium arsenic (GaAs), gallium phosphide (GaP), indium phosphide (InP),indium arsenide (InAs), and/or indium antimonide (InSb); or combinationsthereof. Possible substrates 100 also include a silicon-on-insulator(SOI) substrate. SOI substrates are fabricated using separation byimplantation of oxygen (SIMOX), wafer bonding, and/or other suitablemethods.

The doped regions may be doped with p-type dopants, such as boron orBF₂; n-type dopants, such as phosphorus or arsenic; or combinationsthereof. The doped regions may be formed directly on the substrate 100,in a P-well structure, in an N-well structure, in a dual-well structure,and/or using a raised structure. The substrate 100 may further includevarious active regions, such as regions configured for an N-typemetal-oxide-semiconductor transistor device and regions configured for aP-type metal-oxide-semiconductor transistor device.

Semiconductor fins 110 are formed over the substrate 100 within theLOGIC region 10, and semiconductor fins 210 are formed over thesubstrate 100 within the SRAM region 20. The semiconductor fins 210include semiconductor fins 212, 214, 216, and 218. In some embodiments,the semiconductor fins 212 and 214 may be the same type, and the fins216 and 218 may be the same type. For example, the fins 212 and 214 aren-type semiconductor fins, and the fins 216 and 218 are p-typesemiconductor fins. In FIG. 2C, at least one of the fins 216 and 218includes a bottom portion B and a top portion T disposed on the bottomportion B. The bottom portion B and the top portion T are made ofdifferent materials. For example, the bottom portion B is made ofsilicon, and the top portion T is made of SiGe, and the presentdisclosure is not limited in this respect.

In some embodiments, a pad layer 122 and a mask layer 123 are disposedon the semiconductor fins 110 and 210. In some embodiments, the padlayer 122 may be a thin film comprising silicon oxide formed, forexample, using a thermal oxidation process. The pad layer 122 may act asan adhesion layer between the semiconductor fins 110, 210 and the masklayer 123. In some embodiments, the mask layer 123 is formed of siliconnitride, for example, using low-pressure chemical vapor deposition(LPCVD) or plasma enhanced chemical vapor deposition (PECVD). The masklayer 123 is used as a hard mask during following processes, such asphotolithography.

The semiconductor fins 110 and 210 may be formed by suitable method. Forexample, a pad layer and a mask layer may be blanketed over thesubstrate 100. A patterned photo-sensitive layer is formed over thesubstrate 100. Then, the pad layer, the mask layer, and the substrate100 may be patterned using one or more photolithography processes withthe patterned photo-sensitive layer, including double-patterning ormulti-patterning processes, to form the pad layer 122, the mask layer123, and the semiconductor fins 110 and 210.

Reference is made to FIGS. 3A to 3D. An isolation layer 120 is formedover the substrate 100. In some embodiments, the isolation layer 120 isformed to conformally cover the semiconductor fins 110 and 210 bysuitable deposition process, such as atomic layer deposition (ALD).Thus, plural trenches 125 are formed in the isolation layer 120 andbetween the semiconductor fins 110 and 210. For example, some trenches125 are formed between the fins 110, and some other trenches 125 areformed between the fins 212 and 214. In some embodiments, a thickness ofthe isolation layer 120 is about 12 nm to about 19 nm, and the presentdisclosure is not limited in this respect.

However, in some embodiments, if two adjacent fins are too close, theisolation layer 120 may be filled in the space between the fins. Forexample, in FIG. 3C, since the semiconductor fins 216 and 218 are closeenough, the isolation layer 120 is filled in the space between thesemiconductor fins 216 and 218. That is, no trench is formed between thesemiconductor fins 216 and 218. Similar structures also presents in someof the semiconductor fins 110 within the LOGIC region 10, and are notrepeated herein for simplicity.

Reference is made to FIGS. 4A to 4D. A patterned mask layer 130 isformed over the substrate 100 and covers the isolation layer 120. Themask layer 130 is filled in the trenches 125 in the isolation layer 120.In some embodiments, the mask layer 130 includes an opening 132 thatexposes parts of isolation layer 120 within the LOGIC region 10. Statedifferently, the opening 132 exposes parts of the semiconductor fins 110covered by the isolation layer 120. One or more etching process(es) areperformed through the opening 132 to remove parts of the semiconductorfins 110 and the isolation layer 120 through the opening 132. As aresult, a recess 135 is formed over the substrate 100 within the LOGICregion 10, in which the recess 135 exposes parts of the substrate 100within the LOGIC region 10. At this stage, the SRAM region 20 is coveredby the mask layer 130.

In some embodiments, the etching process may include dry etchingprocess, wet etching process, and/or combination thereof. The recessingprocess may also include a selective wet etch or a selective dry etch. Awet etching solution includes a tetramethylammonium hydroxide (TMAH), aHF/HNO₃/CH₃COOH solution, or other suitable solution. The dry and wetetching processes have etching parameters that can be tuned, such asetchants used, etching temperature, etching solution concentration,etching pressure, source power, RF bias voltage, RF bias power, etchantflow rate, and other suitable parameters. For example, a wet etchingsolution may include NH₄OH, KOH (potassium hydroxide), HF (hydrofluoricacid), TMAH (tetramethylammonium hydroxide), other suitable wet etchingsolutions, or combinations thereof. Dry etching processes include abiased plasma etching process that uses a chlorine-based chemistry.Other dry etchant gasses include CF₄, NF₃, SF₆, and He. Dry etching mayalso be performed anisotropically using such mechanisms as DRIE (deepreactive-ion etching).

Reference is made to FIGS. 5A to 5D. The mask layer 130 of FIGS. 4A to4D is removed. Accordingly, the trenches 125 are exposed. Then, adielectric layer 140 is formed over the substrate 100 and filling thetrenches 125 and the recess 135. In some embodiments, the portions ofthe dielectric layer 140 filled in the trenches 125 may be referred toas dummy fins 145. The dummy fins 145 are formed between some of thesemiconductor fins 110 and 210. For example, a dummy fin 145 is formedbetween the semiconductor fins 212 and 214, and another dummy fin 145 isformed between the semiconductor fins 214 and 216, as shown in FIG. 5C.

In some embodiments, the dielectric layer 140 may include siliconnitride (SiN), oxynitride, silicon carbon (SiC), silicon oxynitride(SiON), oxide, SiO₂, Si₃N₄, SiOCN, and the like and may be formed bymethods utilized to form such a layer, such as CVD, plasma enhanced CVD,sputter, and other methods known in the art.

Reference is made to FIGS. 6A to 6D. A mask layer 150 is formed over thesubstrate 100 and covers the isolation layer 120 and the dielectriclayer 140. The mask layer 150 includes plural openings 155 that exposeparts of the isolation layer 120, and parts of the semiconductor fins216 and 218. One or more etching process(es) are performed to remove theexposed portions of the semiconductor fins 216 and 218. As a result,plural recesses 156 are formed in the isolation layer 120. At thisstage, the LOGIC region 10 is covered by the mask layer 150. Therecesses 156 are defined by the patterned semiconductor fins 210 and theisolation layer 120.

Reference is made to FIGS. 7A to 7D. The mask layer 150 of FIGS. 6A to6D is removed. A dielectric layer 160 is formed over the substrate 100and filling the recesses 156. Then, a CMP process is performed to removethe excessive dielectric layer 160 until the semiconductor fins 110 and210 are exposed. From other perspectives, the removed portions of thesemiconductor fins 216 and 218 are replaced by the dielectric layer 160,and the dielectric layer 160 carries the substantially original shapesof the semiconductor fins 216 and 218. Thus, the dielectric layer 160 inthe recesses 156 may also be referred to as dielectric fins 160. Thedielectric fins 160 may include dielectric material, such as siliconnitride (SiN), oxynitride, silicon carbon (SiC), silicon oxynitride(SiON), oxide, SiO₂, Si₃N₄, SiOCN.

Reference is made to FIGS. 8A to 8F, in that FIG. 8E is across-sectional view taking along line E-E of FIG. 8C, and FIG. 8F is across-sectional view taking along line F-F of FIG. 8C. It is noted thatthe dielectric fins 160 may be separated into a dielectric fins 161,162, and 163 for explanation. An etching process is performed to removeparts of the isolation layer 120. As a result, parts of thesemiconductor fins 110 and 210 are exposed from the isolation layer 120.The remained portions of the isolation layer 120 are labeled as 122, andare referred to as isolation structure 122 in later discussions. Theisolation structure 122 is disposed over the substrate 100 and incontact with the semiconductor fins 110 and 210, and the dielectric fins160.

The top surface 1221 of the isolation structure 122 is in a positionlower than the top surface 1451 of the dummy fins 145, the top surface1101 of the semiconductor fins 110, the top surfaces 2121, 2141, 2161,and 2181 of the semiconductor fins 212, 214, 216, and 218, and the topsurfaces 1611, 1621, and 1631 of the dielectric fins 161, 162, and 163.State differently, the height of the isolation structure 122 is lowerthan the heights of the semiconductor fins 210 and the dielectric fins160. The dummy fins 145 are engaged in parts of the isolation structure122, and the bottom surface 1452 of the dummy fins 145 is spaced fromthe substrate 100 by the isolation structure 122.

In FIGS. 8A and 8C, since the dummy fins 145, the semiconductor fins 110and 210, the dielectric fins 160 are planarized during the processdescribed in FIGS. 7A to 7D, the top surface 1451 of the dummy fins 145,the top surface 1101 of the semiconductor fins 110, the top surfaces2121, 2141, 2161, and 2181 of the semiconductor fins 212, 214, 216, and218, and the top surfaces 1611, 1621, and 1631 of the dielectric fins161, 162, and 163 are substantially coplanar.

Reference is made to FIGS. 8C and 8E. The semiconductor fin 216 includesa base portion 216A and two protruding portions 216B and 216C protrudingupward from the base portion 216B. The dielectric fin 161 is disposedbetween and in contact with the protruding portions 216B and 216C. Fromother perspectives, the base portion 216A of the semiconductor fin 216extends under the dielectric fin 161. Further, the dielectric fin 161 isconnected to the sidewall 2163 of the protruding portion 216B and thesidewall 2164 of the protruding portion 216C. The semiconductor fin 216and the dielectric fin 161 can be collectively referred to as a finstructure 300.

Reference is made to FIGS. 8C and 8F. The semiconductor fin 218 includesa base portion 218A and a protruding portion 218B protruding upward fromthe base portion 216B. The dielectric fins 162 and 163 are disposed overthe base portion 216A and are disposed on opposite sides of theprotruding portion 218B of the semiconductor fin 218. From otherperspectives, the base portion 218A of the semiconductor fin 218 extendsunder the dielectric fins 162 and 163. As shown in FIG. 8C, the sidewall1622 of the dielectric fin 162 and the sidewall 2185 of the base portion218A of the semiconductor fin 218 are substantially coplanar. Theinterface 2186 between the bottom of the dielectric fin 218 and theisolation structure 122 is below the top surface 1221 of the isolationstructure 122. Similar features also present in the dielectric fin 163,and are not repeated herein. The semiconductor fin 218 and thedielectric fins 162 and 163 can be collectively referred to as a finstructure 310.

Referring back to FIG. 8D, the width W1 of the semiconductor fin 216 issubstantially equal to the width W2 of the dielectric fin 161. Also, thewidth W3 of the semiconductor fin 218, the width W4 of the dielectricfin 162, and the width W5 of the dielectric fin 163 are substantiallyequal. The sidewall 2162 of the semiconductor fin 216 and the sidewall1612 of the dielectric fin 161 are substantially coplanar, in which thesidewall 2162 is connected to the sidewall 2163 of the semiconductor fin216. The sidewall 2182 of the semiconductor fin 218, the sidewall 1622of the dielectric fin 162, and the sidewall 1632 of the dielectric fin163 are substantially coplanar.

Reference is made to FIGS. 9A to 9D. A dielectric layer 170 is formedover the substrate 100 and conformally covers the structure of FIGS. 8Aand 8C, i.e., the semiconductor fins 110 and 210, the dielectric fins161, 162, and 163, the dummy fins 145, and the isolation structure 122.The dielectric layer 170 may act as gate dielectric in later process.The dielectric layer 170 may include, for example, a high-k dielectricmaterial such as metal oxides, metal nitrides, metal silicates,transition metal-oxides, transition metal-nitrides, transitionmetal-silicates, oxynitrides of metals, metal aluminates, zirconiumsilicate, zirconium aluminate, or combinations thereof.

Reference is made to FIGS. 10A to 10D. Plural dummy gates 180 are formedover the dielectric layer 170, in which the dummy gates 180 cross thesemiconductor fins 110 and 210, the dielectric fins 161, 162, and 163,and the dummy fins 145. In some embodiments, mask layers 182 and 184 areformed over the dummy gates 180. The mask layers 182 and 184 acts as ahard mask during the patterning process of the dummy gates 180 and mayact as a hard mask during the following processes, such as etching. Insome embodiments, the mask layers 182 and 184 may include silicon oxide,silicon nitride and/or silicon oxynitride.

In some embodiments, the dummy gates 180 may includepolycrystalline-silicon (poly-Si) or poly-crystalline silicon-germanium(poly-SiGe). Further, the dummy gates may be doped poly-silicon withuniform or non-uniform doping. In some embodiments, the dummy gates 180may be formed by, for example, forming a dummy gate material layer overthe dielectric layer 170. Patterned masks, such as mask layers 182 and184, are formed over the stack of gate dielectric layer and dummy gatematerial layer. Then, the dummy gate material layer may be patternedusing one or more etching processes, such as one or more dry plasmaetching processes or one or more wet etching processes. During theetching process, the patterned mask may act as an etching mask. At leastone parameter, such as etchant, etching temperature, etching solutionconcentration, etching pressure, source power, radio frequency (RF) biasvoltage, etchant flow rate, of the patterning (or etching) recipe can betuned. For example, dry etching process, such as plasma etching, may beused to etch the dummy gate material layer and the gate dielectric untilthe semiconductor fins 110 and 210 are exposed.

Reference is made to FIGS. 11A to 11D. Gate spacer structures includingplural gate spacers 190 on opposite sidewalls of the dummy gates 180 areformed. In some embodiments, at least one of the gate spacers 190includes single or multiple layers. The gate spacers 190 can be formedby blanket depositing one or more dielectric layer(s) (not shown) on thepreviously formed structure. The dielectric layer(s) may include siliconnitride (SiN), oxynitride, silicon carbon (SiC), silicon oxynitride(SiON), oxide, and the like. The gate spacers 190 may be formed bymethods such as CVD, plasma enhanced CVD, sputter, or the like. The gatespacers 190 may then be patterned, such as by one or more etch processesto remove horizontal portions of the gate spacers 190 from thehorizontal surfaces of the structure.

The dielectric layer 170 exposed from the dummy gates 180 and the gatespacers 190 are removed by suitable process, such as etching. Theremained portions of the dielectric layer 170 are disposed under thedummy gates 180 and the gate spacers 190. Thus, the remained portions ofthe dielectric layer 170 may be referred to as gate dielectrics 170.Also, the dummy gates 180 and the remained dielectric 170 maycollectively be referred to as dummy gate stacks 185.

Portions of the semiconductor fins 110 and 210, the dummy fins 145, andthe dielectric fins 160 are exposed after the dielectric layer 170 arepartially removed. Then, plural source/drain features 200 arerespectively formed over the semiconductor fins 110 and 210 of thesubstrate 100. In some embodiments, the source/drain features 200 are incontact with the dummy fins 145, such that the formation of thesource/drain features 200 are easily to be controlled.

In some embodiments, the source/drain features 200 may be epitaxystructures, and may also be referred to as epitaxy features 200. Thesource/drain features 200 may be formed using one or more epitaxy orepitaxial (epi) processes, such that Si features, SiGe features, and/orother suitable features can be formed in a crystalline state on thesemiconductor fins 110 and 210. In some embodiments, the source/drainfeatures 200 may be cladding over the semiconductor fins 110 and 210.

In some embodiments, lattice constants of the source/drain features 200are different from lattice constants of the semiconductor fins 110 and210, such that channels in the semiconductor fins 210 are strained orstressed to enable carrier mobility of the semiconductor device andenhance the device performance. In some embodiments, the source/drainfeatures 200 may include semiconductor material such as germanium (Ge)or silicon (Si); or compound semiconductor materials, such as galliumarsenide (GaAs), aluminum gallium arsenide (AlGaAs), silicon germanium(SiGe), silicon carbide (SiC), or gallium arsenide phosphide (GaAsP).

The epitaxy processes include CVD deposition techniques (e.g.,vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)),molecular beam epitaxy, and/or other suitable processes. The epitaxyprocess may use gaseous and/or liquid precursors, which interact withthe composition of the semiconductor fins 110 (e.g., silicon). Thesource/drain features 200 may be in-situ doped. The doping speciesinclude P-type dopants, such as boron or BF₂; N-type dopants, such asphosphorus or arsenic; and/or other suitable dopants includingcombinations thereof. If the source/drain features 200 are not in-situdoped, a second implantation process (i.e., a junction implant process)is performed to dope the source/drain features 200. One or moreannealing processes may be performed to activate the source/drainfeatures 200. The annealing processes include rapid thermal annealing(RTA) and/or laser annealing processes.

In FIGS. 11C and 11D, the source/drain features 200 may be separated insource/drain features 201, 202, and 203 for explanation. In someembodiments, the source/drain features 201 and 202 over thesemiconductor fins 212 and 214 may include the same doping-type, and thesource/drain feature 203 over the semiconductor fin 214 may includedoping-type different from that of the source/drain features 201 and202. For example, the source/drain features 201 and 202 may be n-type,and source/drain feature 203 may be p-type, and vise versa.

Reference is made to FIGS. 12A to 12D. An etching stop layer 215 isformed over the substrate 100 and covers the source/drain features 200,and an interlayer dielectric 220 is formed over the etching stop layer215. Then, a CMP process is performed to remove the excessive interlayerdielectric 220, and the mask layers 182 and 184 (referring to FIGS. 10Ato 10D) until the dummy gate stacks 185 are exposed.

In some embodiments, the interlayer dielectric 220 may include siliconnitride, silicon oxynitride, silicon oxycarbonitride, silicon carbide,silicon germanium, or combinations thereof. The interlayer dielectric220 may be formed by a suitable technique, such as CVD, ALD and spin-oncoating. In some embodiments, air gaps may be created in the interlayerdielectric 220.

Then, a replacement gate (RPG) process scheme is employed. The dummygate stacks 185 are replaced with gate stacks 230. For example, thedummy gate stacks 185 are removed to from a plurality of gate trenches.The dummy gate stacks 185 are removed by a selective etch process,including a selective wet etch or a selective dry etch, and carries asubstantially vertical profile of the gate spacers 190. The gatetrenches expose portions of the semiconductor fins 110 and 210 of thesubstrate 100. Then, the gate stacks 230 are formed respectively in thegate trenches and cover the semiconductor fins 110 and 210 of thesubstrate 100.

The gate stacks 230 include an interfacial layer (not shown), gatedielectrics 232 formed over the interfacial layer, and gate metals 234formed over the gate dielectrics 232. The gate dielectrics 232, as usedand described herein, include dielectric materials having a highdielectric constant, for example, greater than that of thermal siliconoxide (˜3.9). The gate metals 234 may include a metal, metal alloy,and/or metal silicide.

In some embodiments, the gate metals 234 included in the gate stacks 230may include a single layer or alternatively a multi-layer structure,such as various combinations of a metal layer with a work function toenhance the device performance (work function metal layer), liner layer,wetting layer, adhesion layer and a conductive layer of metal, metalalloy or metal silicide. For example, the gate metals 234 may be ann-type or p-type work function layer. Exemplary p-type work functionmetals include TiN, TaN, Ru, Mo, Al, WN, ZrSi₂, MoSi₂, TaSi₂, NiSi₂, WN,other suitable p-type work function materials, or combinations thereof.Exemplary n-type work function metals include Ti, Ag, TaAl, TaAlC,TiAIN, TaC, TaCN, TaSiN, Mn, Zr, other suitable n-type work functionmaterials, or combinations thereof. The work function layer may includea plurality of layers. The work function layer(s) may be deposited byCVD, PVD, electro-plating and/or other suitable process.

In some embodiments, the interfacial layer may include a dielectricmaterial such as silicon oxide (SiO₂), HfSiO, and/or silicon oxynitride(SiON). The interfacial layer may be formed by chemical oxidation,thermal oxidation, ALD, CVD, and/or other suitable method. The gatedielectrics 232 may include a high-K dielectric layer such as hafniumoxide (HfO₂). Alternatively, the gate dielectrics 232 may include otherhigh-K dielectrics, such as TiO₂, HfZrO, Ta₂O₃, HfSiO₄, ZrO₂, ZrSiO₂,LaO, AlO, ZrO, TiO, Ta₂O₅, Y₂O₃, SrTiO₃ (STO), BaTiO₃ (BTO), BaZrO,HfZrO, HfLaO, HfSiO, LaSiO, AlSiO, HfTaO, HfTiO, (Ba,Sr)TiO₃ (BST),Al₂O₃, Si₃N₄, oxynitrides (SiON), combinations thereof, or othersuitable material. The gate dielectrics 232 may be formed by ALD, PVD,CVD, oxidation, and/or other suitable methods.

Reference is made to FIGS. 13A to 13D. For the ease of watching, thecross-section of FIGS. 13A and 13B are taking along line L-L of FIGS.12A and 12B, respectively. An etching process is performed to removeportions of the gate stacks 230. During the etching process, pluralopenings 235 are formed in the gate stacks 230. In some embodiments, theopenings 235 expose at least portions of the dummy fins 145, as shown inFIG. 13A.

Then, plural isolation features 240 are formed in the openings 235. Insome embodiments, the isolation features 240 may be formed by depositinga dielectric layer blanketing the substrate 100. Then, a CMP process isperformed to remove the excessive dielectric layer until the gate stacks230 are exposed. Some of the isolation features 240 are in contact withthe gate dielectric 170 and over the dummy fins 145. That is, some ofthe isolation features 240 are align with the dummy fins 145.

Reference is made to FIGS. 14A to 14D. An etching process is performedto remove portions of the interlayer dielectric 220 and the etching stoplayer 215. Thus, plural openings 245 are formed in the interlayerdielectric 220 and the etching stop layer 215 to expose the source/drainfeatures 200 and the dummy fins 145.

Then, plural contacts 250 are formed in the openings 245. The contacts250 may be formed by depositing a conductive material layer over thesubstrate 100 and following with a CMP process until the gate stacks 230are exposed. In some embodiments, the contacts 250 are in contact withthe source/drain features 200 and the dummy fins 145. For example, inFIG. 14C, one of the contacts 250 is in contact with the source/drainfeatures 200 over the semiconductor fins 212, 214, and 216, and is incontact with the dummy fins 145 between the semiconductor fins 212, 214,and 216. Since the source/drain features 200 are in contact with thedummy fins 145, the contacts 250 may have improved quality. The dummyfins 145 can support the contacts 250, such that the contacts 250 do notextend further into a space between the source/drain features 200. Insome embodiments, at least one of the contacts 250 includes a barrierlayer 251 and conductive layer 252. In some embodiments, the conductivelayer 252 may include suitable metal, such as TiN, WN, TaN, or Ru, whichperforms in a p-type FinFET. In some alternative embodiments, the metallayer may include suitable metal, such as Ti, Ag, Al, TiAl, TiAlN,TiAlC, TiAlCN, TaC, TaCN, TaSiN, Mn, or Zr, which performs in an n-typeFinFET. In some other embodiments, the contacts 250 may be multi-layerincluding, work function layers, liner layers, interface layers, seedlayers, adhesion layers, barrier layers and so on.

According to aforementioned embodiments, plural semiconductor fins arepartially removed to form a recess defined by the semiconductor fins andan isolation structure connected to the semiconductor fins. A dielectriclayer is formed to fill the recess. Accordingly, plural dielectric finsare formed in the recess, in which the dielectric fins are in contactwith the semiconductor fins. Moreover, plural dummy fins are formedbetween two adjacent semiconductor fins and engaged in the isolationstructure. With such configurations, the structural strength may beimproved. Also, plural epitaxy structures are formed over thesemiconductor fins and in contact with the dummy fins. As a result, theformation of the epitaxy structures is easily to be controlled, and thecontact formed over the epitaxy structures may have improved quality.

An embodiment of the present disclosure is a semiconductor deviceincludes a substrate, a first dielectric fin, a semiconductor fin, ametal gate structure, an epitaxy structure, and a contact etch stoplayer. The first dielectric fin is disposed over the substrate. Thesemiconductor fin is disposed over the substrate, in which along alengthwise direction of the first dielectric fin and the semiconductorfin, the first dielectric fin is in contact with a first sidewall of thesemiconductor fin. The metal gate structure crosses the first dielectricfin and the semiconductor fin. The epitaxy structure is over and incontact with the semiconductor fin. The contact etch stop layer is overand in contact with first dielectric fin.

An embodiment of the present disclosure is a semiconductor deviceincludes a substrate, a first dielectric fin, a second dielectric fin, asemiconductor fin, and a metal gate structure. The first dielectric finand a second dielectric fin are disposed over the substrate, in which abottom surface of the first dielectric fin is lower than a bottomsurface of the second dielectric fin. The semiconductor fin is disposedover the substrate, in which the semiconductor fin is between the firstdielectric fin and the second dielectric fin, and a distance between thefirst dielectric fin and the semiconductor fin is less than a distancebetween the second dielectric fin and the semiconductor fin. The metalgate structure crosses the first dielectric fin, the second dielectricfin, and the semiconductor fin.

An embodiment of the present disclosure is a semiconductor deviceincludes substrate, a first dielectric fin, first epitaxy structure,contact etch stop layer, and a metal gate structure. The firstdielectric fin is over the substrate. The first epitaxy structure isover the first semiconductor fin, in which a first sidewall of the firstepitaxy structure is in contact with the first dielectric fin. Thecontact etch stop layer is over the first epitaxy structure, in which asecond sidewall of the first epitaxy structure farthest to the firstsidewall of the first epitaxy structure is in contact with the contactetch stop layer. The metal gate structure crosses the semiconductor finand the first dielectric fin.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a substrate;a first dielectric fin disposed over the substrate; a semiconductor findisposed over the substrate, wherein along a lengthwise direction of thefirst dielectric fin and the semiconductor fin, the first dielectric finis in contact with a first sidewall of the semiconductor fin; a metalgate structure crossing the first dielectric fin and the semiconductorfin; an epitaxy structure over and in contact with the semiconductorfin; and a contact etch stop layer over and in contact with firstdielectric fin.
 2. The semiconductor device of claim 1, wherein a widthof the first dielectric fin is substantially the same as width of thesemiconductor fin.
 3. The semiconductor device of claim 1, wherein thefirst dielectric fin is free from coverage of the epitaxy structure. 4.The semiconductor device of claim 1, further comprising a seconddielectric fin disposed over the substrate, wherein the seconddielectric fin is in contact with a second sidewall of the semiconductorfin opposite to the first sidewall of the semiconductor fin.
 5. Thesemiconductor device of claim 1, wherein a sidewall of the firstdielectric fin, a sidewall of the semiconductor fin, and a sidewall ofthe second dielectric fin are coterminous.
 6. The semiconductor deviceof claim 1, further comprising a shallow trench isolation (STI)structure adjacent to the first dielectric fin, wherein a bottom surfaceof the STI structure is lower than a bottom surface of the firstdielectric fin.
 7. The semiconductor device of claim 6, wherein the STIstructure crosses an interface between the first dielectric fin and thesemiconductor fin.
 8. A semiconductor device, comprising: a substrate; afirst dielectric fin and a second dielectric fin disposed over thesubstrate, wherein a bottom surface of the first dielectric fin is lowerthan a bottom surface of the second dielectric fin; a semiconductor findisposed over the substrate, wherein the semiconductor fin is betweenthe first dielectric fin and the second dielectric fin, and a distancebetween the first dielectric fin and the semiconductor fin is less thana distance between the second dielectric fin and the semiconductor fin;and a metal gate structure crossing the first dielectric fin, the seconddielectric fin, and the semiconductor fin.
 9. The semiconductor deviceof claim 8, further comprising a contact over and in contact with thefirst dielectric fin, wherein the second dielectric fin is separatedfrom the contact.
 10. The semiconductor device of claim 9, furthercomprising a contact etch stop layer extending from a sidewall of thecontact to a sidewall of the second dielectric fin.
 11. Thesemiconductor device of claim 8, wherein the semiconductor fin comprisesa base portion extending to a bottom surface of the second dielectricfin.
 12. The semiconductor device of claim 8, further comprising anepitaxy structure over the semiconductor fin, wherein a distance betweenthe epitaxy structure and the first dielectric fin is less than adistance between the epitaxy structure and the second dielectric fin.13. The semiconductor device of claim 8, wherein along a lengthwisedirection of the first dielectric fin and the second dielectric fin, thefirst dielectric fin is longer than the second dielectric fin.
 14. Asemiconductor device, comprising: a substrate comprising a semiconductorfin; a first dielectric fin over the substrate; a first epitaxystructure over the first semiconductor fin, wherein a first sidewall ofthe first epitaxy structure is in contact with the first dielectric fin;a contact etch stop layer over the first epitaxy structure, wherein asecond sidewall of the first epitaxy structure farthest from the firstsidewall of the first epitaxy structure is in contact with the contactetch stop layer; and a metal gate structure crossing the semiconductorfin and the first dielectric fin.
 15. The semiconductor device of claim14, further comprising a second dielectric fin over the substrate, thesemiconductor fin being between the first and second dielectric fins.16. The semiconductor device of claim 15, wherein the contact etch stoplayer is in contact with a sidewall of the second dielectric fin. 17.The semiconductor device of claim 16, wherein the contact etch stoplayer is further in contact with a top surface of the second dielectricfin.
 18. The semiconductor device of claim 15, further comprising aninterlayer dielectric layer between the semiconductor fin and the seconddielectric fin, wherein the second dielectric fin is separated from thefirst epitaxy structure by the interlayer dielectric layer.
 19. Thesemiconductor device of claim 14, wherein the contact etch stop layer isin contact with a top surface of the first dielectric fin.
 20. Thesemiconductor device of claim 14, wherein the first sidewall of thefirst epitaxy structure is free from coverage by the contact etch stoplayer.